Question about oem ECU

Black kNight

I wanted to ask
why most cars A/F ration from factory comes rich ???
and can someone help with more Info about A/F ratio so I can understand

Thanks

MikeGTO

Most modern cars are set to run rich (at full throttle) because it's safer for the engine and in some cases, safer for the pollution controls. With a rich mixture there is less risk of damaging engine knock, and it helps keep the cat converter temperatures under control.

During normal driving, the car should not be rich or lean, it will fine-tune itself to just about the right mixture (if everything is working right). So it should only be rich under hard acceleration.

Black kNight

ok
thanks alot
but how to read the A/F ratio !! I mean what is the correct ratio for Turbo cars and NA cars it have to be ??

MikeGTO

Well I'm no expert but people generally need a wideband O2 sensor to measure the A/F ratio accurately. This is what dyno shops use for measuring A/F ratio during dyno runs.

For NA cars, and these are just approximations based on what I remember about LS1 V8s, they typically run about 12.0:1 at full throttle with factory tune & settings. This will vary some based on engine type and how the factory tune is programmed. Aftermarket tuning will usually lean this out some to make more power, somewhere in the range of 12.8:1 is usually considered a pretty good target to make good power while still being safe for a NA engine.

I don't have any real experience with turbos, but in general, turbo cars and supercharged cars will be tuned a little bit richer than NA cars, since the higher cylinder pressures with the turbo make it more prone to knock. Just throwing a number out there, but I would think a turbo or supercharged car would probably be tuned somewhere around 12.0 :1, and I wouldn't feel very safe leaning it out more than that.

Black kNight

Thanks Mike for the Help

smalltuner

12.8 - 13 AFR is the best target for N/A cars

thats what we do in the N/A 350z

HP Logic

To really understand AFR's and how they are figured for a particular setup....you must have some general understanding of flame-front propagation....but heres the cliff notes...

Gasoline burns most efficiently at a 14.7:1 ratio...but this is not safe nor efficient when building power...for NA cars 12.5-13.5 is the accepted AFR....turbo cars will benefit from a richer mixture due to cylinder pressure and latent heat...11.5:1 is a good start...but each setup is different...and with Race gas these mixtures like to be a bit leaner....due to its slower burning/higher octane rating....there is a huge spectrum of variables that dictate the proper settings for fuel on each car...so this is just a general rule of thumb!

-Jack

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Jack Cecil
HorsepowerLogic.com

Black kNight

thanks Jack and smalltuner for the Information

K20A2_S

the main reason is b/c they don't know where teh car is going, your a/f ratios will vary greatly running in 100 degree houston weather, than 30 degree Chicago weather........

When the air is that dense in the cold you need more fuel to compensate.........so I'm guessing they "tune" the stock ECU to handle those type of A/F rations b/c it's better to run rich then lean like most have mentioned.....

Uprev

Nope, the car has an Air Intake Temp sensor. It will adjust the fuel according to the volume of air, which is calculated via density and flow.

The reason why some car run rich from the factory is because no two cars are alike. We've had cars that are 100% stock and have less than 20k miles on them that have come in at 16:1 at full throttle. Others that have been 11:1 at full throttle. Add aftermarket parts and the situation can be even worse. The ECU adjusts based on what it sees. If there is a bad sensor or a leak then it can't do a great job. Often there is a stuck injector, or a single injector that is flowing too much or too little.

If it's really out of hand, and the ECU targets aren't being hit, it will throw a CEL. It rarely happens on a totally stock car, but we've seen it. Something as simple as an exhaust gasket leak can cause a car to run totally off target.